1. Technical Field
The present application relates to a thermoelectric generation unit including a thermoelectric conversion element which converts heat into electric power. The present disclosure also relates to a thermoelectric generation system including a plurality of thermoelectric generation units.
2. Description of the Related Art
A thermoelectric conversion element is an element which can convert heat into electric power, or electric power into heat. A thermoelectric conversion element made of a thermoelectric material that exhibits the Seebeck effect is able to obtain thermal energy from a heat source at a relatively low temperature (e.g., 200 degrees Celsius or less), and convert it into electric power. With a thermoelectric generation technique based on such a thermoelectric conversion element, it is possible to collect and effectively utilize thermal energy which would conventionally have been dumped unused into the ambient in the form of steam, hot water, exhaust gas, or the like.
Hereinafter, a thermoelectric conversion element which is made of a thermoelectric material may be referred to as a “thermoelectric generator”. A generic thermoelectric generator has a so-called “π structure” in which a p-type semiconductor and an n-type semiconductor of mutually different carrier electrical polarities are combined (for example, Japanese Laid-Open Patent Publication No. 2013-016685). In a “π structure” thermoelectric generator, a p-type semiconductor and an n-type semiconductor are connected electrically in series, and thermally in parallel. In a “π structure”, the direction of temperature gradient and the direction of electric current flow are parallel or antiparallel to each other. This makes it necessary to provide output terminals at the electrodes on the high-temperature heat source side or the low-temperature heat source side. Therefore, complicated wiring structure will be required for a plurality of thermoelectric generators each having a “π structure” to be connected in electrical series.
International Publication No. 2008/056466 (hereinafter “Patent Document 1”) discloses a thermoelectric generator which includes a stacked body sandwiched between a first electrode and a second electrode opposing each other, the stacked body including bismuth layers and metal layers of a different metal from bismuth being alternately stacked. In the thermoelectric generator disclosed in Patent Document 1, the planes of stacking are inclined with respect to the direction of a line connecting the first electrode and the second electrode. Moreover, tube-type thermoelectric generators are disclosed in International Publication No. 2012/014366 (hereinafter “Patent Document 2”) and Kanno et al., preprints from the 72nd Symposium of the Japan Society of Applied Physics, 30a-F-14 “A Tubular Electric Power Generator Using Off-Diagonal Thermoelectric Effects” (2011) and A. Sakai et al., International conference on thermoelectrics 2012 “Enhancement in performance of the tubular thermoelectric generator (TTEG)” (2012).